A miniature (e.g. 12 mm long and wide) trackball control device includes a ball with an exposed top that can be manually moved to turn the ball about horizontal axes. Two coding shafts that are rotatably mounted about perpendicular horizontal axes, each turns in proportion to rotation of the ball about its corresponding axis. A control signal generator detects rotation of each coding shaft to generate control signals. In one application, the control signals move a cursor up and down or from side to side on a screen, such as a screen of a portable telephone.
Various designs have been proposed for signal generators that generate signals indicating the amount and direction of rotation of each of two coding shafts. Some factors in the choice of a signal generator are its reliability, whether or not it consumes electricity in its standby or rest state, and its complexity and cost. The ease of connection of the signal generators to an electronic device that uses the signals such as an electronic display on which the cursor image moves, is also important.
In many applications it is desirable to provide an entry switch or button which the user presses in order to enter a choice, as to enter a choice when a cursor has reached a particular position on the screen by manipulation of the ball. This can be accomplished by depressing the ball to operate a switch.
A trackball control device of low cost and reliable design would be of value, especially if the signal generators for detecting rotation of the coding shafts and the connection of the signal generator with another electronic device such as a display, were of reliable and low cost design.